1. Field of Invention
The present invention relates to a driving method for dynamically driving a field sequential color liquid crystal display by passive arrays.
2. Description of Related Arts
Field sequential color liquid crystal display generally divides a color image (frame) into three images (fields) with red (R), green (G), and blue (B) in sequence based on time, and then switches those images (fields) in sequence at high-speed to form a color image (frame). If three primary colors i.e. R, G, and B are used, the time for which each field is shown will be ⅓ of the time for which one frame is shown, i.e., three fields constitute one frame period. If two or four colors are used, the time for which each field is shown will be ½ or ¼ of the time for which one frame is shown, i.e., two or four fields constitute one frame period, and so on. On the other hand, the driving method for a liquid crystal display primarily consists of two ways, i.e., active arrays driving and passive arrays (or simple arrays) driving. The latter is also referred as dynamical driving, with multiple COMs and multiple SEGs being intersected and forming the arrays. When a certain COM is being scanned, a selected voltage (ON voltage) will be applied on the liquid crystal pixels which are selected by the SEG voltage, and an unselected voltage (OFF voltage) will be applied on the unselected liquid crystal pixels.
The general structure of the existing dynamic driven field sequential color liquid crystal display includes a liquid crystal display screen, a backlight, a backlight driver and a liquid crystal display screen driver, wherein the backlight is set at the bottom of the liquid crystal display screen, and the backlight driver and the liquid crystal display screen driver drive the backlight and the liquid crystal display screen respectively. For the driving method for dynamically driving a field sequential color liquid crystal display, FIG. 20 is an example of driving with ½ duty cycle in a positive type (the liquid crystal screen presents a transmission state in the case of OFF voltage). Obviously, there are also similar issues below for driving with other duty cycles. As illustrated, when the same red driving waveforms are input from COM1 and COM2 respectively, the liquid crystal pixels are turned on within the red-light district and turned off within the cyan-light district. In order to eliminate the DC component, the polarities of the driving waveforms in the same field are reversed at least once. Because there is a delay response time for the liquid crystal materials relative to the driving voltage, when the ON or OFF voltage is applied on the liquid crystal pixels, there are one descendant area and one ascendant area of the light transmission intensity thereof corresponding to the ON response time or the OFF response time, and the main factor affecting the uniformity of color is the ascendant area (i.e., the dotted line in the figure, which is referred as the amount of light leakage). As the COM1 and COM2 are in different periods of time, the ascendant area for the COM1 is in the cyan area, and the ascendant area for the COM2 is in the red area. Although the red of COM1 has cyan components, the red transmission intensity for COM1 is larger than that for COM2, and the amount of cyan light leakage for COM1 is less than that for COM2. Thus, it results in the red of COM1 and the red of COM2 in the same image being different. Of course, the same cases will occur when other colors are shown. If the negative type is used (the liquid crystal screen presents transmission state in the case of ON voltage), as shown in FIG. 21, when the driving waveforms with the same color such as red driving waveforms are input from COM1 and COM2, the red descendant area for COM2 will be in the subsequent cyan area, while there will be no cyan light leakage for COM1. This causes the cumulative light transmission intensities of each color of the COM1 and COM2 to be different, which ultimately results in the illustrated red be different. Consequently, both the purity and uniformity of the colors are changed, and the uniformity of the brightness for the display is also changed with them. If such displays with other duty cycles such as ⅓, ¼, ⅛, . . . , 1/N are used, there will also be similar issues.